feat(bulk-upload): add BulkDocumentEditLayout component with save handler

State-owner for the bulk upload flow:
- N=0: full-panel BulkDropZone
- N=1: title + shared metadata (no switcher/scope cards)
- N≥2: FileSwitcherStrip + per-file ScopeCard + shared ScopeCard
Save handler chunks files at 10/request, POSTs to /api/documents/quick-upload
with typed metadata JSON part, tracks progress, redirects to /documents.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/document/ScopeCard.svelte

@@ -12,6 +12,7 @@ let {
 
 <div
 	data-testid="scope-card"
+	data-variant={variant}
 	class="rounded-sm border p-4
 		{variant === 'per-file'
 		? 'border-brand-mint bg-brand-mint/10'